live load definition

[bnrg]

Hi all,
I am working with an OSHA specc on ladders that requires that the rungs be able to hold a 200 pound live load. No acceleration level specified. Can some one explain what is the meaning of live load in this case?
Thanks,
Bob

 

[zekeman]

I would ask OSHA for their definition.
Absent that, the actual peak load due to a live load is usually taken as double. The theory is that if you suddenly apply a load to an elastic system you would double the strain on it, hence causing double the load.

 

[Cockroach]

Live load is the dynamic load, typically anything other than static or dead weight. The static load would be the individual weight of members comprising your assembly, for example. Dynamic is more like the variation in worker weight using the ladder, maximum allowable load carried by an end user, that sort of thing.

In general it is the varying load, in your case, the heaviest bearing intensity the ladder as an overall structure is capable of sustaining. In buildings, dynamic load usually refers to the maximum number of people the floor can withstand to bring it equal to your design factor of safety.

I would take the fattest possible worker, 250 lbf, and the maximum possible lift capability buddy can handle safely on the ladder, say half his weight. Build your ladder to suit 375 lbf dynamic load, factor of safety of two or three.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[SlideRuleEra]

From an ASD (Allowable Stress Design) structural viewpoint the live load is the static weight that the ladder is intended to carry (the person will all his/her equipment). The fact that a person moves would be addressed with a second factor, an impact load (which it sounds like you do not have to consider). The weight of the ladder itself is the dead load.

 

[JStephen]

The "live load" means it is the load applied by the worker, in other words, not a permanent load. You wouldn't normally apply any other factors to it.

OSHA ladder regs are based on old ANSI standards, and looking at a less-old ANSI standard, I find it gives AISC-ASD for the allowable stresses for steel ladders.

I seem to recall that the minimum rung size, 3/4" diameter by 16" long, calculates out to be somewhat marginal using A36 steel, but in reality works fine.

You can ask OSHA for an official interpretation, but be prepared to wait months for an answer. I'm still waiting on some ladder questions sent in on February 9th.